Machines which have high speed rotating parts supported by bearings, such as pneumatic tools, often use the exhaust motive fluid for cooling the bearings. Electric tools also generate an air flow to cool the bearings and other rotating parts. These air flows often contain particle contamination such as dirt or grit that may prematurely damage the bearings or rotating parts. In some machines, the bearings that support critical components are provided with complex and expensive sealing mechanisms to prevent particle contamination.
Common bearings used in dirty environments often have a shield between the outer race and the inner race. The shield is typically attached to the stationary race but there is still a clearance gap at the interface between the shield and the rotating race. For certain high speed pneumatic tools, such as grinders for example, dirty motive fluid exhaust can penetrate between the bearing shield and the rotating race. Other known seals typically have an elastomeric lip which rubs on the stationary race to prevent any particle contamination from entering the bearing chamber. However, these known seals generate friction and additional heat due to the rubbing contact. Also the known seals are expensive and not durable.